linux-cve-announce - CVE-2025-38560: x86/sev: Evict cache lines during SNP memory validation

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Message-ID: <2025081906-CVE-2025-38560-d265@gregkh>
Date: Tue, 19 Aug 2025 19:18:07 +0200
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...nel.org>
Subject: CVE-2025-38560: x86/sev: Evict cache lines during SNP memory validation

From: Greg Kroah-Hartman <gregkh@...nel.org>

Description
===========

In the Linux kernel, the following vulnerability has been resolved:

x86/sev: Evict cache lines during SNP memory validation

An SNP cache coherency vulnerability requires a cache line eviction
mitigation when validating memory after a page state change to private.
The specific mitigation is to touch the first and last byte of each 4K
page that is being validated. There is no need to perform the mitigation
when performing a page state change to shared and rescinding validation.

CPUID bit Fn8000001F_EBX[31] defines the COHERENCY_SFW_NO CPUID bit
that, when set, indicates that the software mitigation for this
vulnerability is not needed.

Implement the mitigation and invoke it when validating memory (making it
private) and the COHERENCY_SFW_NO bit is not set, indicating the SNP
guest is vulnerable.

The Linux kernel CVE team has assigned CVE-2025-38560 to this issue.


Affected and fixed versions
===========================

	Fixed in 6.1.148 with commit 1fec416c03d0a64cc21aa04ce4aa14254b017e6a
	Fixed in 6.6.102 with commit 1fb873971e23c35c53823c62809a474a92bc3022
	Fixed in 6.12.42 with commit aed15fc08f15dbb15822b2a0b653f67e76aa0fdf
	Fixed in 6.15.10 with commit a762a4c8d9e768b538b3cc60615361a8cf377de8
	Fixed in 6.16.1 with commit f92af52e6dbd8d066d77beba451e0230482dc45b
	Fixed in 6.17-rc2 with commit 7b306dfa326f70114312b320d083b21fa9481e1e

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2025-38560
will be updated if fixes are backported, please check that for the most
up to date information about this issue.


Affected files
==============

The file(s) affected by this issue are:
	arch/x86/boot/cpuflags.c
	arch/x86/boot/startup/sev-shared.c
	arch/x86/coco/sev/core.c
	arch/x86/include/asm/cpufeatures.h
	arch/x86/include/asm/sev.h
	arch/x86/kernel/cpu/scattered.c


Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/1fec416c03d0a64cc21aa04ce4aa14254b017e6a
	https://git.kernel.org/stable/c/1fb873971e23c35c53823c62809a474a92bc3022
	https://git.kernel.org/stable/c/aed15fc08f15dbb15822b2a0b653f67e76aa0fdf
	https://git.kernel.org/stable/c/a762a4c8d9e768b538b3cc60615361a8cf377de8
	https://git.kernel.org/stable/c/f92af52e6dbd8d066d77beba451e0230482dc45b
	https://git.kernel.org/stable/c/7b306dfa326f70114312b320d083b21fa9481e1e